The present invention is directed to the encoding of data for transmission and subsequent decoding thereof, and is particularly concerned with the encoding of data to place it in a form suitable for transmission via standard television program signals.
In the transmission of digital data, for example from one computer to another, it is common to employ existing communication media where the data is to be transmitted over large distances, and thereby avoid the need for dedicated data transmission lines. For example, the use of telephone lines to communicate data between computers, via modems, is one popular form of data transmission. However, since telephone lines were originally designed for voice grade communications, they offer limited bandwidth capabilities for data communication. As a result, the speed at which data can be transmitted over telephone lines, i.e. the available baud rate, is limited.
In an effort to increase the speed at which data can be efficiently transmitted, other existing forms of transmission media are being evaluated. One such medium is the television communication network. The transmission bandwidth that is available in a standard television channel can readily accommodate the transmission of data at higher rates. Furthermore, the availability of television reception at almost any point within the United States makes television transmission a viable medium for communicating data from any location to another location at a relatively low cost.
Typically, data is transmitted within a television signal by inserting the data in one or more lines of the vertical blanking interval of a standard television field. Since the vertical blanking interval does not contain any video information, i.e., any information pertaining to the image to be reproduced on a television screen, the placement of data on these lines of the signal would not interfere with the normal television program.
The transmission of data via television signals is not without its attendant limitations, however. Foremost among these are the types of noise that can be encountered when the television signal is transmitted through a commonly employed transmission medium, e.g., over the air or through cable. More particularly, in any form of transmission the data is normally subject to random noise that can create errors in individual bits of the data. By encoding the transmitted data with a suitable error checking code, individual bit errors can be readily identified in the received data and corrected. However, in addition to random noise that can cause errors with respect to individual bits, television transmissions are also subject to impulse noise that can delete an entire horizontal line of information. In such a case, error checking codes alone are not effective, since insufficient information is available at the receiving end to detect whether errors are present. Accordingly, it is desirable to provide an encoding technique for data that enables the data to be reliably transmitted via television signals and reconstructed at the receiving end, even when random noise and impulse noise may be present.